HIIT Training or Continuous Aerobic Exercise better for Weight Loss?

An often misunderstood concept which training method is best for weight loss – high intensity interval training (HIIT) or continuous aerobic exercise? Both perform primarily the same thing – increase energy expenditure through physical activity, but which one will benefit you more? Much research has been conducted to attempt to answer this problem.

Substrate Utilization During Exercise

Before I begin to explain both exercise techniques, I first need to explain what we use for energy. During long duration exercise (greater than 30 seconds-2 minutes), we predominantly gain energy from fats and carbohydrate stores. Whenever we breakdown 1 gram of carbohydrate or fat, we burn 4 or 9 calories, respectively. The amount of energy derived from either of these two stores is dependent on the intensity of exercise.

Continuous Aerobic Exercise

Continuous aerobic exercise (CAE) can be defined as maintaining a constant elevated strain on the body for an extended period of time. This paradigm gained traction because when one is working at or below approximately 60% of their maximal oxygen consumption, the major percentage of macronutrient consumption is fat. This is also referred to as the crossover effect; as the intensity of exercise increases, one starts to switch from using predominantly fats to carbohydrates for energy. A major advantage to this training is that you can work at a moderate intensity, which for some may be easy to manage for extended periods of time.

HIIT

High intensity interval training (HIIT) is where one conducts multiple repetitions of high intensity and low intensity cardio. It makes the body work harder for short bursts, recover, and then go back to high intensity. As one is working at a higher intensity, they are therefore utilizing carbohydrate stores for energy. One of the benefits of HIIT training is the increased amount and duration of exercise post exercise oxygen consumption (EPOC). EPOC occurs after every exercise bout, however duration of EPOC is dependent on the duration and intensity of exercise. If you deplete a larger volume of your energy stores, you will require additional oxygen to restore your body to resting energy levels. A disadvantage to HIIT is that one needs to be able to conduct high intensity exercise, therefore if you have any debilitation medical condition (Cardiovascular disease, hypertension, myocardial infarction, COPD, etc) – it is high discouraged.

ASIDE: Current research however is starting to test the inclusion of HIIT for rehabilitation of cardiac patients.

Battle Royale:CAE or HIIT?

So which one is better for weight loss? In an study conducted by Tremblay et al. (1994), they had performed this battle royale. They had two groups of young adults be subjected to either a 20 week endurance training (ET) program or a 15 week HIIT. Surprisingly, although the ET group had burnt a higher amount of total energy, the HIIT group saw a greater reduction in subcutaneous fat. The researchers concluded that “…vigorous exercise favors negative energy and lipid balance to a greater extent than exercise of low to moderate intensity.”

They are not the only group of researchers to show that HIIT training is better than CAE. More recently, Talanian et al. (2006) demonstrated that 7 HIIT sessions over 2 weeks can improve whole body and skeletal muscle’s capacity for fatty acid oxidation during exercise in moderately active women. Therefore, if you want to increase your ability to oxidize fats during exercise, HIIT is the way to go.

Additionally, previously mentioned in this article was the Crossover Concept. A nice review to read on this is by Brooks & Mercier (1994). Figure 1 demonstrates that the crossover between substrates increases with training. Therefore at higher intensities, the major substrate utilized for energy will be fats.

Verdict…

As you can already imagine, the verdict is pretty clear, HIIT will be of greater benefit to someone who wishes to lose weight. It would take less time to burn the same amount of calories by conducting HIIT instead of CAE. Furthermore, you would gain greater training adaptations from HIIT.

At the end of the day, it is all about energy expenditure, and in todays fast pace society, less is more. If you can only spare 30 minutes per session, then HIIT is the way to go. It may take 40-60 minutes to burn the same amount of energy doing continuous moderate intensity exercise.

Although HIIT may be a great way to lose weight, it may be best to not rely on it solely as it may be too difficult to perform consistently 4 times a week. A great way to ease into HIIT is by incorporating it slowly.

For example, maybe try to perform 3 days of moderate intensity cardio for 60 minutes and 1 day of HIIT training for 30 minutes. Gradually increase the amount of HIIT sessions, but do not overdo it. Burning yourself out will sideline you from exercise… and potentially keep yourself from attaining your goals.

In conclusion, hit or miss on HIIT? Definite hit. If you are crammed for time, you can burn more calories doing HIIT than steady state cardio for 30 minutes. Perfect for someone who is constantly on the go!